Method of producing high quality lubricating oils



Feb. 27, 1945. B. K. ENGEL 2,370,297

METHOD OF PRODUCING HIGH QUALITY LUBRICATING OILS Filed Nov. 3, .1942

RAFF/A/ATE NM-PA RAFFlA/IC RECUVERED EXTRA er 50L VENT s04 vzwra; 0/1.

CO0L E R S01. VENT l DEWAXED WAX W/TH T SOLUTION $0045 OIL COOLER COOLER MST/LL50 DIST/l LED DIST/LLED $01. VE/V? SOLVENT 504 IV? NON-FL um 50L urmNoF PARA FFIIV/C SOLVENT a Patented Feb. 27, 1945 METHOD OF PRODUCING HIGH QUALITY LUBRICATING OILS Bruno Kuno Engel, Nockeby, Sweden, assignor to Aktiebolaget Separator-Nobel,

Stockholm,

Sweden, a, corporation of Sweden Application November 3, 1942,- Serial No. 464,384 In Germany November 26,1941

1 Claim. (c1.19c-1s) Thisinvention relates to a method of producing high quality lubricating oils by subjecting mixtures of hydrocarbons containing such oils to de-waxing and refining at low temperature. With the known methods the ,de-waxing of lubricating oil fractions is effected by adding a suitable solvent and then cooling the mixture to a temperature at which the majority of the crystalline wax, solid at ordinary temperature, is precipitated. The solid wax is generally separated from the oil solution by centrifuging or filtering, When using very selective solvents and further cooling the oil solution to low temperature, after it has been liberated from the crystalline wax, anew phase is obtained, the paraflinic lubricating oil hydrocarbons thereby being precipitated in gelatinous semi-solid form and the aromatic and/or naphthenic (substantially non-paraifinic) hydrocarbons remaining in solution. As is well known, the parafiinic hydrocarbons are of very high value as lubricating oils owing to their high viscosity index and low content of polymerizing constituents with high molecular weight. On the other hand, the aromatic and/or naphthenic hydrocarbons are of a certain value with regard to their relatively high viscosity but less valuable as lubricants, because of their strong tendency to form colloidallydissolved asphalts and carbon partices in very fine suspension. Besides, it is also known that especially the high molecular aromatic constituents or the aromaticfractions have a favourable influence not only on the reduction of the pour point of the oil but also on the crystallization of the solid wax particles, so that these become more easily separable by mechanical means owing to the formation of aggregates of large crystals, which may be separated very readily from the oil solution and, in contrast to the fine wax crystals, contain only relatively insignificant amounts of valuable oil constituents.

The most important selective solvents used for the de-waxing of lubricating oils are, e. g., chlorinated hydrocarbons, as methylene chloride, dichlor ethane, etc., or ketones, as acetone, butanone, methyl propyl ketone, etc., either as such, or mixed with each other or with other suitable. solvents. The advantage of these solvents as compared with several other de-waxing agents suggested heretofore, as naphtha, propane, butane, etc., lie in the possibility of reaching a considerably smaller spread between the de-waxing temperature and the pour point ofthe de-waxed lubricating oil. When using dichlor ethane and solventmixtures containing this agent, a negative spread may be obtained in many cases, so that the pour point of the 'de-waxed oil is lower than the temperature at which the de-waxing was carried to 25 0., respectively. In order to increase the yield of oil.with low pour point it is often advantageous to de-oil the petrolatum obtained at the de-waxing by washing it with fresh solvent at low temperature. This is effected by mixing the petrolatum with solvent preferably-pre-cooled in a heat exchanger and re-centrifuging or re-filtering the mixture. When the de-waxing of the oil is combined with such a de-oiling of the wax, a given yield of oil may be obtained, by using a substantially'smaller amount of solvent than at dewaxing in .only one step. Thereby considerably less wax becomes dissolved than is the case in a one-stage process in which a, larger amount of solvent is used. By these means considerable advantages are reached, particularly in respect of the consumption of refrigerating and distilling energy and the reduction of solvent losses. With a view to further reducing the costs the washing may also be carried out in more than two steps. The liquor obtained at the washing, which contains oil and is more or less free from wax, may advantageously partly or wholly be returned to the first step and be used as wax precipitant for precipitating the wax in a new batch of oil.

The wax-free oil solution obtained in the first step, which may contain more or less washing liquor, is now chilled to a temperature of about ,-20 to 0., advantageously 25 to 40 C. The fluid lubricating oil hydrocarbons are thereby precipitated in the form of a semi-solid gelatinous product, whereas the aromatic and/or naphthenic constituents remain in solution. In conformity with the ordinary technical nomenclature the parafiinic lubricating oil hydrocarbons obtained in the second chilling to low temperature will in the following be referred to as raflinate and the aromatic and/or naphthenic constituents remaining in solution as extract." Further, the first step of the process, in which the crystalline wax is removed and is then de-oiled by one or more washing operations, will be referred to as thede-waxing stage, and the second step carried out atlower temperature, in which a separation into rafiinate and extract takes place, as the refining stage. The lower the temperature is at which the refining is carried out, the higher the proportion of parafilnic particles precipitated, and the smaller the amount of aromatic and/or naphthenic particles passing over into the valuable parafiinic lubricating oil phase.

I have found that the economy of the process may be considerably improved by returning the extract obtained in the refining stage, or a part thereof, to the de-waxing process and mixing it with the initial material prior to the separation of the crystalline wax. The extract may be added both prior to, during and after the chilling of the first mixture. Consequently, .the mixture flowing thru the de-waxing plant contains a larger amount of aromatic and/or naphthenic constituents than the original mixture. By the present method the following advantages are obtained. The initial material's artificially increased content of aromatic and/or naphthenic particles (extract) facilitates, as stated in the foregoing the precipitating of the wax in large crystals, which is favourable with regard to the separating of the wax by mechanical means, that is by settling, centrifuging or filtering, and results in higher centrifugal thruput or higher filter rate per unit of filter area. Owing to the formation of easily separable coarse wax aggregates, the degree of dilution may be quite considerably reduced without substantially affecting the rate of separation. Further, with a given yield of de-waxed oil, it becomes possible to work with a considerably smaller amount of solvent in the washing of the petrolatum than is the case when treating fine wax crystals. Using a lower degree of dilution, on the other hand, enables the de-waxing to be effected at a higher temperature than was possible when carrying out the process in the known form, that is without returning the extract. In this way a considerable improvement of the economy of the process is obtained, due not only to the reduction of the amounts of solvent to be used, and the reduction of the loss of solvent at the distillation resulting therefrom, but also to the reduced consumption of refrigerating energy, because a smaller amount of solvent has to be chilled as compared with the known methcds and because the mixture of initial oil and solvent may be de-waxed at a higher temperature than heretofore, and finally on account of the saving of energy at the distillation of the solvent in the recovery plant. It will be understood that the improvement of the economy refers not only to the operation of the plant but also to the plant itself, as the initial cost and the space required for the refrigerating and compressor arrangements and also the separating and distilling apparatus is considerably reduced.

As above indicated, the refining of the waxfree oil solution obtained in the de-waxing and de-oiling stage is carried out by further chilling to IoWtemperature, and centrifuging, filtering, etc. In the continuous process the extract is divided into two batches, the one of which may be used as burning oil or asphalt and the like after removing the solvent, whereas the other is continuously re-cycled to the initial mixture. The amount of extract solution to be re-cycled varies from case to case, and depends on the concentration of the extract in the solution required to improve the structure of the wax to be separated. During the process the amount should of course be kept constant in order not to disturb the equilibrium between aromatic, naphthenic and paraflinic hydrocarbons, and the conditions of temperature and dilution required in the two processes. In case the amount of extract returned becomes too small or too large owing to disturbances in the operation, the said amount may be regulated in simple manner by suitably varying the temperature of 'the refining stage. As a general rule may be stated that the separation of the extract from the raffinate becomes more complete, the lower the refining temperature is. Even if the latter in some cases should entail an increase of the operating costs, such increase is many times outweighed by the advantages mentioned, obtainable by the reduced degree of dilution and the higher separating thruput owing to the presence of the extract by which 'the crystallization is improved.

After reaching a state of equilibrium, a given amount of extract continuously circulates in the process, whereas the rest, corresponding to the amount fed to the process with the fresh oil, is continuously withdrawn in the refining process. The amount of extract returned need not be added as such in pure form, but may be added to the initial oil or the initial oil solution in dissolved form after being passed thru a heat exchanger. the high degree of dilution, it has the same efl'ect as pure solvent in the de-waxing. The only products which need be subjected to distillation for removing of the solvent are thus the rafiinate, the portion of extract not returned to the process, and the petrolatum obtained in the dewaxing stage after the washing. The amount of solvent to be distilled is thus not larger than the one which would be required, if the process were carried out without returning the portion of extract to be circulated. It will be understood that when starting the combined de-waxing and refining processes not only a part but the whole quantity of extract may be returned with a view to obtaining the stated eflfectby which the crystallization is ameliorated.

The process is diagrammatically illustrated, in its most simplified embodiment, in the drawing, which shows a flow sheet of the process, wherein, in the first step of the process, there is added, to the initial oil, a preferential solvent for the oil, the same solvent recovered in the wax-deolling step, and non-paraifinic extract, containing some of the same solvent, recovered in the step for separating such extract from paraffinic non-fluid raifinate. It will be understood that the solvent recovered, by distillation, from the raflinate, from the portion of the extract not returned to the first step of the process, and from the deolled wax, may also be utilized as added solvent in the first step of the process.

In order to increase the rate of separation of the wax and the raffinate respectively above that mentioned in the foregoing, it is in some cases advantageous not to add all extract, or washing liquor from the de-waxing stage respectively or both solutions, to the initial material already at the beginning of the process, but in two or more steps at dropping temperature. In other cases it is an advantage not to separate the wax in one step but by fractional separation in several steps at dropping temperature. It may also be advantageous not to extract all of the oil obtained in the de-waxing at low temperature but only part of it, and to add the extract thereby obtained to the initial solution.

What I claim and desire to protect by Letters Patent is:

The hereindescribed method of producing high quality lubricating oils from hydrocarbon oil containing wax constituents which on cooling pre- Experience has shown that, owing to cipitate in solid form, which comprises adding to said hydrocarbon oil, solvent and oil that are products, as hereinafter specified, of later steps of the process and cooling to a temperature at which crystalline wax is precipitated in large crystals, separating the precipitated wax with some oil from the bulk of the solution of oil and solvent, cooling the thus dewaxed solution to such substantially lower temperature than that in the above specified dewaxing operation as to precipitate a parafiinic non-fluid rafiinate while maintaining the remaining non-parafinic extract 

